Adhesive composition

ABSTRACT

An adhesive composition of the present invention contains, as a main composition, a polymer obtained by copolymerizing a monomer composition containing a monomer having a maleimide group, and further contains a thermal polymerization inhibitor. As a result, it is possible to provide an adhesive composition that allows forming an adhesive layer that is excellently dissolved after the adhesive layer has been subjected to a high-temperature process.

This Nonprovisional application claims priority under 35 U.S.C. §119(a)on Patent Applications No. 2008-158391 filed in Japan on Jun. 17, 2008and No. 2009-074898 filed in Japan on Mar. 25, 2009, the entire contentsof which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an adhesive composition, a filmadhesive, and a heat treatment method. More specifically, the presentinvention relates to (i) an adhesive composition and a film adhesive,each for temporarily fixing a sheet or a protection board to asemiconductor product, in a step of carrying out processing such asgrinding of semiconductor products (e.g., semiconductor wafer), opticalproducts, and the like, and (ii) a heat treatment method using theadhesive composition.

Background Art

In recent years, due to multiple functioning of mobile phones, digitalAV devices, IC cards, and the like, demands have been increasing fordownsizing, reduction in thickness, and high integration ofsemiconductor silicon chips (hereinafter referred to as “chips”). Forexample, the reduction of thickness is demanded for integrated circuitsin which a plurality of chips are integrated, as typified by CSP (chipsize package) and MCP (multi-chip package). Among these integratedcircuits, a system-in-package (SiP) in which a plurality ofsemiconductor chips are mounted in a single semiconductor package hasbecome an extremely important technique in order to accomplishdownsizing, reduction in thickness, and high integration of chips thatare installed in the semiconductor package. The downsizing, reduction inthickness and high integration enables realization of multiplefunctioning, downsizing, and reduction of weight of electronic devices.

In order to respond to the needs for a thin product, it is required toreduce the thickness of a chip to not more than 150 mm. Further, it isrequired to process a chip so that its thickness is reduced to not morethan 100 mm for the CSP and the MCP, and not more than 50 mm for the ICcard.

Conventionally, SiP products are manufactured by use of a method inwhich respective bumps (electrodes) provided on each of stacked chipsare wired to a circuit board by a wire bonding technique. In order torespond to the demand for the reduction in thickness and highintegration, a through-hole electrode technique is required, not thewire bonding technique. The through-hole electrode technique is atechnique in which (i) chips each having a through-hole electrode arestacked and (ii) a bump is formed on a backside of the chips thusstacked.

A thin chip is manufactured by, for example, in a method as follows: (i)a high purity single crystal silicon or the like is sliced to a waferform, (ii) a predetermined circuit pattern of an IC or the like isformed on a surface of the wafer by etching the surface of the wafer sothat an integrated circuit is built, (iii) a back surface of thesemiconductor wafer thus obtained is grinded by use of a grinder, and(iv) after the semiconductor wafer is grinded to a predeterminedthickness, the semiconductor wafer is diced so as to form a chip shape.At this time, the predetermined thickness is around a range of 100 μm to600 μm. Further, in a case where a through-hole electrode is to beformed, the wafer is grinded to a thickness of around a range of 50 μmto 100 μm.

In the manufacture of the semiconductor chip, the semiconductor waferreadily breaks if external force is given to the wafer in the grindingstep or at the time when the wafer is carried to the dicing step. Thisis because the semiconductor wafer is thin and fragile, and becausecircuit patterns are unlevel. Moreover, in the grinding step, purifiedwater is used to clean the back surface of the semiconductor wafer forremoving grinding dust and heat generated at the time of grinding, whilegrinding process is carried out. At this time, there is the need toprevent contamination of a circuit pattern surface due to the purifiedwater used in cleaning.

Accordingly, in order to protect the circuit pattern surface of thesemiconductor wafer and prevent breakage of the semiconductor wafer, afilm adhesive for processing is attached on the circuit pattern surfacewhile the grinding process is carried out.

Moreover, at the time of the dicing, the semiconductor wafer is diced ina state in which a protection sheet is attached to a back surface of thesemiconductor wafer so that the semiconductor wafer is fixed. Chipsobtained by the dicing are pushed up by use of a needle from a film basematerial side, and are fixed on a die pad.

Known types of film adhesives for processing and protection sheets assuch include, for example, ones in which an adhesive layer made of anadhesive composition is provided on a base material film such aspolyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP),or ethylene-vinyl acetate copolymer (EVA) (for example: Japanese PatentApplication Publication, Tokukai, No. 2003-173993 A (Publication Date:Jun. 20, 2003; Japanese Patent Application Publication, Tokukai, No.2001-279208 A (Publication Date: Oct. 10, 2001); Japanese PatentApplication Publication, Tokukai, No. 2003-292931 A (Publication Date:Oct. 15, 2003)).

An arrangement has also been disclosed (Japanese Patent ApplicationPublication, Tokukai, No. 2002-203821 A (Publication Date: Jul. 19,2002)) in which a protection board is used instead of using the filmadhesive for processing or the protection sheet. The protection board isan aluminum nitride-boron nitride pore sintered body impregnated withladder-type silicone oligomer. In the arrangement, this protection boardand the semiconductor wafer are adhered together by use of athermoplastic film. There is also a method in which a material such asalumina, aluminum nitride, boron nitride, or silicon carbide, each ofwhich has substantially the same thermal expansivity as thesemiconductor wafer, is used as the protection board, and thermoplasticresin such as polyimide is used as an adhesive for attaching theprotection board to the semiconductor wafer (Japanese Patent ApplicationPublication, Tokukai, No. 2001-77304 A (Publication Date: Mar. 23,2001)). This method suggests applying the adhesive in a form of a filmhaving a thickness in a range of 10 μm to 100 μm. As a method forforming the film, this method suggests that an adhesive composition isapplied by spin coating and then dried so that an obtained film has athickness of not more than 20 μm.

Moreover, due to multilayer interconnection of semiconductor elements, aprocess is conducted such that: (i) a protection board is adhered, byuse of the adhesive composition, to a surface of the semiconductor waferon which a circuit is formed; (ii) a back surface of the semiconductorwafer is polished; (iii) the back surface thus polished is etched toform a mirror plane; and (iv) a back surface circuit is formed on themirror plane. In this case, the protection board is adhered to thesemiconductor wafer until the back surface circuit is formed (JapanesePatent Application Publication, Tokukaisho, No. 61-158145 A (PublicationDate: Jul. 17, 1986)).

SUMMARY OF INVENTION

Technical Problem

However, the following problems occur in a case where the conventionalfilm adhesive for processing and the like are used in steps whichrequire high-temperature processing and high vacuum processing, as likein formation of the through-hole electrode: a problem of poor adhesioncaused by insufficient adhesive strength in a high temperatureenvironment or generation of gas in a high vacuum environment; or aproblem of poor stripping such as residue remaining at the time ofstripping following the high-temperature processing.

For example, in the formation of the through-hole electrode, whensemiconductor chips are to be connected to each other after formation ofa bump on each of the semiconductor chips, a process is required inwhich heat is applied to the semiconductor chips to approximately 200°C., and further the semiconductor chips is processed in a high vacuumstate. However, the adhesive composition which constructs an adhesivelayer of a protection tape, according to Japanese Patent ApplicationPublication, Tokukai, No. 2003-173993 A (Publication Date: Jun. 20,2003; Japanese Patent Application Publication, Tokukai, No. 2001-279208A (Publication Date: Oct. 10, 2001), has no resistance against such ahigh temperature of 200° C. Moreover, gas is generated due toapplication of heat. This gas causes the poor adhesion.

The thin semiconductor wafer requires to be stripped off from theprotection board after the grinding and dicing. However, the adhesivecomposition, which constructs an adhesive layer of a protection tape,disclosed in Japanese Patent Application Publication, Tokukai, No.2003-292931 A (Publication Date: Oct. 15, 2003), is an epoxy resincomposition. At a high temperature of 200° C., the epoxy resin changesin quality and cures. This causes residue to remain at the time ofstripping, thereby causing poor stripping.

Further, in the thermoplastic film, according to Japanese PatentApplication Publication, Tokukai, No. 2002-203821 A (Publication Date:Jul. 19, 2002) and Japanese Patent Application Publication, Tokukai, No.2001-77304 A (Publication Date: Mar. 23, 2001), used for adhering aprotection board to a semiconductor wafer, gas derived from absorbedmoisture is generated. This causes the problem of poor adhesion. Theprocessing method of the semiconductor substrate, according to JapanesePatent Application Publication, Tokukaisho, No. 61-158145 A (PublicationDate: Jul. 17, 1986), carries out a mirror surfacing process by use ofan etching liquid and formation of a metal film by vacuum deposition. Inorder to carry out these processes, the adhesive composition foradhering a protection board to a semiconductor wafer requires heatresistance and stripping property. However, Japanese Patent ApplicationPublication, Tokukaisho, No. 61-158145 A (Publication Date: Jul. 17,1986) includes no disclosure regarding formation of the adhesivecomposition.

Studies conducted by inventors of the present invention resulted inthat, in processing of a semiconductor wafer and a chip, an adhesive,which uses an acrylic resin material, is preferably used, due to itscrack resistance. However, the inventors found that the followingproblems occur even when the adhesive, which uses such an acrylic resinmaterial, is used.

(1) Adhesive strength is weak in a high temperature environment, due toan occurrence of a bubble-form strip on an adhesive surface at the timewhen the adhesive layer and the protection board are thermallycompressed together, caused by generation of gas from moisture absorbedby the adhesive layer. Such generation of gas causes problems, not onlythat the adhesive strength is weakened in the high temperatureenvironment, but also difficulty in production and maintenance of avacuum environment in a case where processing is carried out undervacuum conditions.

(2) In a case where there is a step at which a semiconductor wafer hascontact with an alkaline liquid such as an alkaline slurry or analkaline developer, a contact surface of the adhesive compositiondeteriorates due to stripping, melting, diffusion or the like caused bythe alkaline liquid.

(3) In a case where the adhesive is heated to approximately 200° C., theadhesive composition changes in quality due to low heat resistance. Thiscauses poor stripping such as formation of an insoluble substance in astripping solution.

The present invention is accomplished in view of the above problems. Anobject of the present invention is to provide an adhesive composition(i) which has high adhesive strength in a high temperature environment(especially at a temperature of 200° C. to 250° C.), high heatresistance, and alkaline resistance, (ii) which has low moistureabsorbency, and (iii) which can be easily stripped off from asemiconductor wafer, a chip, and the like even after the adhesivecomposition has been processed in a high temperature environment and/orin a high vacuum environment (hereinafter, simply referred to as a“high-temperature process”).

In order to achieve the above object, an adhesive composition of thepresent invention is an adhesive composition whose main component is apolymer obtained by copolymerizing a monomer composition containing amonomer having a maleimide group and which further contains a thermalpolymerization inhibitor.

Additional objects, features, and strengths of the present inventionwill be made clear by the description below. Further, the advantages ofthe present invention will be evident from the following explanation inreference to the drawings.

DESCRIPTION OF EMBODIMENTS

[Adhesive Composition]

One embodiment of an adhesive composition of the present invention isdescribed below.

The adhesive composition of the present invention is an adhesivecomposition whose main component is a polymer obtained by copolymerizinga monomer composition containing a monomer (hereinafter referred to as amaleimide group-containing monomer) having a maleimide group and whichfurther contains a thermal polymerization inhibitor.

A concrete purpose of the adhesive composition of the present inventionis not especially limited provided that the adhesive composition is usedas an adhesive. The present embodiment deals with, as an example, a casewhere the adhesive composition of the present invention is used fortemporarily adhering a semiconductor wafer to a support plate in a wafersupport system.

In the present specification, “main component” means that a content ofthe component is larger than those of any other components contained inthe adhesive composition of the present invention. Accordingly, thecontent of the main component is not limited as long as the content islargest among those of components contained in the adhesive composition.However, the content of the main component is preferably not less than50 parts by weight but not more than 100 parts by weight, morepreferably not less than 70 parts by weight but not more than 100 partsby weight, where a total amount of the adhesive composition is 100 partsby weight. In a case where the content of the main component is not lessthan 50 parts by weight, the adhesive composition of the presentinvention successfully exhibits effects of high heat resistance, highadhesive strength in a high temperature environment (especially, 200° C.to 250° C.), alkaline resistance, and easiness in stripping after ahigh-temperature process such as a heat treatment in which the adhesivecomposition is heated at 250° C. for 1 hour. In the presentspecification and the like, “support plate” indicates a substrate usedfor protecting a semiconductor wafer in such a manner that the supportplate is attached to the semiconductor wafer while the semiconductorwafer is being grinded, so that occurrences of cracks and distortion ofthe semiconductor wafer are prevented.

(Thermal Polymerization Inhibitor)

The adhesive composition of the present invention contains a thermalpolymerization inhibitor. The thermal polymerization inhibitor is amaterial effective to prevent a radical polymerization reaction due toheat. Since reaction of the thermal polymerization inhibitor with aradical more preferentially proceeds than reaction of a radical with amonomer, polymerization is inhibited. On this account, in the adhesivecomposition of the present invention, a polymerization reaction of theadhesive composition in a high temperature environment (especially, 250°C. to 350° C.) is restrained. As a result, even after the adhesivecomposition has been subjected to a high-temperature process in whichthe adhesive composition is heated at 250° C. for 1 hour, the adhesivecomposition can be easily dissolved. Consequently, it is possible toeasily strip off an adhesive layer made from the adhesive compositioneven after the adhesive layer has been subjected to the high-temperatureprocess and to restrain that a residue of the adhesive layer remains.

The thermal polymerization inhibitor is not especially limited providedthat the thermal polymerization inhibitor effectively prevents a radicalpolymerization reaction due to heat. However, the thermal polymerizationinhibitor is preferably a phenolic thermal polymerization inhibitor.

Examples of the thermal polymerization inhibitor encompass: pyrogallol;benzoquinone; hydroquinone, methylene blue; tert-butylcatechol;monobenzyl ether; methylhydroquinone; amylquinone; amyloxy hydroquinone;n-butylphenol; phenol; hydroquinone monopropyl ether;4,4′-(1-methylethylidene) bis(2-methylphenol); 4,4′-(1-methylethylidene)bis(2,6-dimethylphenol);4,4′-[1-[4-(1-(4-hydroxyphenyl)-1-methylethyl)phenyl]ethylidene]bisphenol; 4,4′,4″-ethylidenetris(2-methylphenol),4,4′,4″-ethylidenetrisphenol;1,1,3-tris(2,5-dimethyl-4-hydroxyphenyl)-3-phenylpropan,2,6-di-tert-butyl-4-methylphenol; 2,2′-methylene bis(4-methyl-6-tertbutylphenol); 4,4′-butylidene bis(3-methyl-6-tert butylphenol);4,4′-tiobis(3-methyl-6-tert butylphenol); 3,9-bis[2-(3-(3-tertbutyl-4-hydroxy-5-methylphenyl)-propionyloxy)-1,1-dimet hylethyl]-2,4,8,10-tetraoxaspiro(5,5)undecane; triethyleneglycol-bis-3-(3-tertbutyl-4-hydroxy-5-methylphenyl)propionate; n-octyl -3-(3,5-di-tertbutyl-4-hydroxyphenyl)propionate; pentaerythritoltetrakis[3-(3,5-di-tert butyl-4-hydroxyphenyl)propionate] (product name:IRGANOX1010, manufactured by Ciba Speciality Chemicals Corporation);tris(3,5-di-tert butylhydroxybenzyl) isocyanurate; and tiodiethylenebis[3-(3,5-di tert butyl-4-hydroxyphenyl)propionate]. Among them,phenolic thermal polymerization inhibitors are preferable.

A content of the thermal polymerization inhibitor may be determined asappropriate in accordance with a polymer contained as a main component,a purpose of the adhesive composition, and a usage environment. However,the thermal polymerization inhibitor is preferably contained by not lessthan 0.1 wt % but not more than 10.0 wt %, more preferably not less than0.5 wt % but not more than 7.0 wt %, and most preferably not less than1.0 wt % but not more than 5.0 wt %. By containing the thermalpolymerization inhibitor within the above range, the adhesivecomposition can successfully exhibit an effect to restrainpolymerization due to heat so that the adhesive layer that has beensubjected to the high-temperature process can be more easily strippedoff. Further, the containing of the inhibitor within the above range canprevent an occurrence of cracks.

(Maleimide Group-Containing Monomer)

The adhesive composition according to the present invention contains, inthe monomer composition, a maleimide group-containing monomer. Theadhesive composition obtained by containing the maleimidegroup-containing monomer has an imide ring (a heterocyclic ring havingan imide group) in a main chain of a polymer that is a main component ofthe adhesive composition. This improves the heat resistance and theadhesive strength in a high temperature environment (especially, 200° C.to 250° C.), of the adhesive composition. Further, an adhesive layermade from the adhesive composition can be easily stripped off even afterthe adhesive layer has been subjected to a high-temperature process suchas a heat treatment in which the adhesive layer is heated at 250° C. for1 hour.

The maleimide group-containing monomer is not especially limitedprovided that the monomer has a maleimide group and can be copolymerizedwith other monomer components. However, the maleimide group-containingmonomer is preferably a compound represented by General Formula (1):

(where R¹ through R³ independently represent a hydrogen atom or a C1through C20 organic group, and the organic group may contain an oxygenatom, a nitrogen atom, a sulfur atom, and a halogen atom.)

The organic group represented by R¹ or R² in General Formula (1) ispreferably a hydrogen atom, a methyl group, or an ethyl group. Amongthem, a hydrogen atom is more preferable.

The organic group represented by R³ in General Formula (1) is preferablya straight or branched alkyl group, an alicyclic hydrocarbon group, anaryl group, an aralkyl group, or an organic group having a maleimidegroup. Among them, the alkyl group, the alicyclic hydrocarbon group, andthe aryl group are more preferable.

Here, an “aliphatic series” is a relative concept with respect to anaromatic series and defined as a group, a compound, or the like havingno aromatic property. For example, the “alicyclic hydrocarbon group”indicates a monocyclic hydrocarbon group or a polycyclic hydrocarbongroup having no aromatic property.

The alkyl group, the alicyclic hydrocarbon group, or the aryl group,represented by R³, may have a substituent group. The substituent groupis not especially limited, and may be, for example, a halogen atom, astraight or branched C1 to C6 alkyl group, a C3 to C6 alicyclichydrocarbon group, or the like. Here, “having a substituent group” meansthat part of or all hydrogen atoms in the alkyl group, the alicyclichydrocarbon group, or the aryl group is/are substituted with asubstituent group. The halogen atom may be, for example, a fluorineatom, a chlorine atom, a bromine atom, an iodine atom, or the like. Thefluorine atom is especially preferable as the halogen atom.

Examples of the alkyl group represented by R³ encompass a methyl group,an ethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a lauryl group, and a stearylgroup. Among them, the methyl group is preferable.

Examples of a maleimide group-containing monomer in which the organicgroup represented by R³ is the alkyl group encompass: N-methylmaleimide;N-ethylmaleimide; N-n-propylmaleimide; N-isopropylmaleimide;N-n-butylmaleimide; N-isobutylmaleimide; N-sec-butylmaleimide;N-tert-butylmaleimide; N-n-pentylmaleimide; N-n-hexylmaleimide;N-n-heptylmaleirhide; N-n-octylmaleimide; N-laurylmaleimide; andN-stearylmaleimide. Among them, the N-methylmaleimide is preferable interms of stability in industrial supply and heat resistance.

The alicyclic hydrocarbon group represented by R³ may be a cyclopropylgroup, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, acycloheptyl group, or a cyclooctyl group. Among them, the cyclohexylgroup is preferable.

Examples of a maleimide group-containing monomer in which the organicgroup represented by R³ is the alicyclic hydrocarbon group encompass:N-cyclopropylmaleimide; N-cyclobutylmaleimide; N-cyclopentylmaleimide;N-cyclohexylmaleimide; N-cycloheptylmaleimide; andN-cyclooctylmaleimide. Among them, the N-cyclohexylmaleimide ispreferable in terms of stability in industrial supply and heatresistance.

The aryl group represented by R³ may be a phenyl group, a methylphenylgroup, or the like. Among them, the phenyl group is preferable.

Examples of a maleimide group-containing monomer in which the organicgroup represented by R³ is the aryl group encompass: N-phenylmaleimide;N-m-methylphenylmaleimide; N-o-methylphenylmaleimide; andN-p-methylphenylmaleimide. Among them, the N-phenylmaleimide ispreferable in terms of stability in industrial supply and heatresistance.

In addition to the above examples, there are further other examples ofthe maleimide group-containing monomer such as: N-benzylmaleimide;N-phenethylmaleimide; 1-methyl-2,4-bismaleimidebenzene; N,N′-m-phenylenebismaleimide; N,N′-p-phenylene bismaleimide; N,N′-m-toluylenebismaleimide; N,N′-4,4-biphenylene bismaleimide;N,N′-4,4-(3,3′-dimethyl-biphenylene)bismaleimide;N,N′-4,4-(3,3′-dimethyl diphenyl methane)bismaleimide; N,N′-4,4-(3-3′-diethyl diphenyl methane)bismaleimide;N,N′-4,4-diphenylmethane bismaleimide; N,N′-4,4-diphenylpropanebismaleimide; N,N′-3-3′-diphenylsulfone bismaleimide; N,N′-4,4-diphenylether bismaleimide; and the like.

These maleimide group-containing monomers constituting a polymer that isa main component of the adhesive composition may be used solely or incombination.

A mixed amount of the maleimide group-containing monomer is not limitedprovided that copolymerization reaction with other compounds containedin the monomer composition proceeds, and may be set as appropriate inaccordance with aimed properties of the adhesive composition, such asaimed adhesive strength and heat resistance. However, the maleimidegroup-containing monomer is preferably contained in the monomercomposition by not less than 1.0 wt % but not more than 25 wt %, morepreferably not less than 5 wt % but not more than 20 wt %. In a casewhere the maleimide group-containing monomer is contained by not lessthan 1.0 wt %, it is possible to obtain an adhesive in which the heatresistance and the adhesive strength in a high temperature environmentare more improved. Further, in a case where the maleimidegroup-containing monomer is contained by not more than 25 wt %, it ispossible to obtain an adhesive that can be more easily stripped off evenafter the adhesive has been subjected to a high-temperature process.

(Styrene)

The adhesive composition according to the present embodiment may furthercontain styrene in the monomer composition. Properties of the styrene donot change even in a high temperature environment of not less than 200°C. This allows improvement in the heat resistance of the adhesivecomposition.

In a case where the monomer composition contains styrene, a mixed amountof the styrene is not limited provided that copolymerization reaction ofthe styrene with other compounds contained in the monomer compositionproceeds, and may be set as appropriate in accordance with aimedproperties of the adhesive composition, such as aimed adhesive strengthand heat resistance. However, the styrene is preferably mixed in themonomer composition by not less than 1 part by weight but not more than60 parts by weight, more preferably not less than 20 parts by weight butnot more than 60 parts by weight, where a total amount of the monomercomposition containing the styrene and the maleimide group-containingmonomer is 100 parts by weight. In a case where the styrene is mixed bynot less than 1 part by weight, it is possible to obtain an adhesive inwhich the heat resistance is more improved. Further, in a case where thestyrene is mixed by not more than 60 parts by weight, it is possible toobtain an adhesive in which crack resistance is improved.

(Styrene Block Segment)

The polymer that is the main component of the adhesive compositionaccording to the present embodiment may have a styrene block segment.

An adhesive composition whose main component is a polymer having astyrene block segment prevents generation of gas on an interface betweenthe adhesive composition and an adhered object. Therefore, it ispossible to obtain an adhesive composition which prevents interlayerstripping of the adhesive composition caused by generation of gas on theinterface at the time of heating and vacuuming, and which has animproved adhesive strength in a high temperature environment.

Moreover, dissociation of molecular chains of the adhesive compositionis suppressed in the high temperature environment. This makes itpossible to prevent quality changes of the adhesive composition in thehigh temperature environment. Hence, the adhesive strength of theadhesive composition improves, and furthermore, an adhesive layer madefrom the adhesive composition can be easily stripped even after theadhesive layer has been processed at a high temperature.

Further, the formation of the styrene in a block form causes a pseudosea-island structure in a coating film made from the adhesivecomposition, thereby forming a relatively hard region and a relativelysoft region. This can cause stress relief due to heat. As a result, itis possible to restrain an occurrence of cracks while high-temperatureresistance of the adhesive composition is maintained. Moreover, therestraining of the occurrence of cracks can further restrain intrusionsof solvent and dust from the cracks. This reduces defects in processesand improves a production yield in the processes.

The “styrene block segment” in the present specification is a part inwhich the styrene is copolymerized by units of blocks in the polymer.Addition of the styrene after polymerization has been initiated causesthe styrene to be formed in a block unit just including the styrene.This is because, at this point, copolymerization of other components hasbeen mostly completed. As such, the styrene block segment is a blockcopolymer obtained by polymerization of just the styrene that is addedafter the initiation of polymerization of other monomer components.

The formation of the styrene block segment from the styrene is carriedout as follows. That is, all or part of styrene used in production ofthe adhesive composition is added, at once or stepwise, to acopolymerization reaction system, that is, a reaction container or thelike in which copolymerization of a remaining part of the styrene andother monomer components including the maleimide group-containingmonomer is being carried out.

An amount of styrene for forming a styrene block segment is adjusted byan amount of styrene to be added after the copolymerization reaction hasbeen initiated. The amount may be set as appropriate in accordance withaimed properties of the adhesive composition, such as aimed adhesivestrength, heat resistance, and the like, but is preferably not less than1 part by weight but not more than 100 parts by weight where a totalamount of styrene used in the production of the adhesive composition ofthe present embodiment is 100 parts by weight.

The styrene to be added after the initiation of the copolymerizationreaction is preferably added at once. That is, it is preferable that allthe styrene be added at once. Further, it is preferable that the styrenebe added before half the time required for the copolymerization reactionhas elapsed. This causes the styrene to be copolymerized in closecontact with each other, thereby favorably forming the styrene blocksegment in the adhesive composition.

(Alkyl(Meth)Acrylate)

The adhesive composition of the present invention may further contain analkyl(meth)acrylate in the monomer composition.

In the present specification, the alkyl(meth)acrylate denotes acryliclong-chain alkyl ester having a C15 to C20 alkyl group, and acrylicalkyl ester having a C1 to C14 alkyl group.

By containing the alkyl(meth)acrylate in the monomer composition, acontent ratio of alkyl chains included in the polymer mainly containedin the adhesive composition increases. This can cause stress relief inthe adhesive composition, thereby resulting in that an occurrence ofcracks can be restrained while high-temperature resistance ismaintained. Further, the restraining of the occurrence of cracks canrestrain intrusion of solvent and dust from the cracks. Consequently,this reduces defects in processes and improves a production yield in theprocesses.

Examples of the acrylic long-chain alkyl ester encompass alkyl esters ofan acrylic or methacrylic acid whose alkyl group is an n-pentadecylgroup, an n-hexadecyl group, an n-heptadecyl group, an n-octadecylgroup, an n-nonadecyl group, n-eicosyl group, or the like. Note that thealkyl group of the acrylic long-chain alkyl ester may be straight orbranched.

The acrylic alkyl ester having the C1 to C14 alkyl group may be publiclyknown acrylic alkyl esters that are used in conventional (meth)acrylicadhesives. Examples of these acrylic alkyl esters are, for example,alkyl esters of an acrylic or methacrylic acid whose alkyl group is amethyl group, an ethyl group, a propyl group, a butyl group, a2-ethylhexyl group, an isooctyl group, an isononyl group, an isodecylgroup, a dodecyl group, a tridecyl group, a lauryl group, or the like.

These alkyl(meth)acrylates for constituting the polymer that is a maincomponent of the adhesive composition may be used solely or incombination.

A mixed amount of the alkyl(meth)acrylate is not limited provided thatcopolymerization with other compounds contained in the monomercomposition proceeds, and may be set as appropriate in accordance withaimed properties of the adhesive composition, such as intended adhesivestrength and heat resistance. However, the mixed amount of thealkyl(meth)acrylate is preferably not less than 10 parts by weight butnot more than 90 parts by weight, more preferably not less than 20 partsby weight but not more than 80 parts by weight, where a total amount ofthe monomer composition containing the alkyl(meth)acrylate and themaleimide group-containing monomer is 100 parts by weight. The mixedamount of the alkyl(meth)acrylate of not less than 10 parts by weightallows an improvement in flexibility and crack resistance of an obtainedadhesive. In a case where the mixed amount of the alkyl(meth)acrylate isnot more than 90 parts by weight, it is possible to obtain an adhesivein which a decrease in heat resistance, poor stripping, and moistureabsorption are suppressed.

The adhesive composition of the present invention may contain, in themonomer composition, both the styrene and the alkyl(meth)acrylate. In acase where the monomer composition contains both the styrene and thealkyl(meth)acrylate, a mass ratio of the styrene and thealkyl(meth)acrylate in the monomer composition is not limited providedthat essential properties of the present invention are not lost.However, the mass ratio of the alkyl(meth)acrylate with respect to thestyrene is preferably in a range from 0.1 to 3, more preferably in arange from 0.5 to 2.5. The range allows the adhesive composition to havegood heat resistance, adhesiveness, and the like properties.

(Bifunctional Monomer)

The adhesive composition of the present invention further contains abifunctional monomer. By containing the bifunctional monomer,constituent molecules of an obtained adhesive composition arecross-linked via the bifunctional monomer. A three-dimensional structureis generated due to the crosslinking, which causes an increase inmass-average molecular weight of the adhesive composition. It isgenerally known in the technical field of adhesives that the increase inthe mass-average molecular weight of the constituent molecules improvesinternal energy of the adhesive composition. It is also known that theinternal energy is one cause of an obtained strength of the adhesivestrength in the high temperature environment. Moreover, the increase inthe mass-average molecular weight of the adhesive composition causes arise in an apparent glass transition point. As a result of this, theadhesive strength improves. That is to say, by further containing thebifunctional monomer in the monomer composition, the mass-averagemolecular weight of the adhesive composition increases, which causes theadhesive strength to increase in the high temperature environment.

Further, by containing the bifunctional monomer in the monomercomposition, it is possible to suppress an occurrence of dissociationbetween molecular chains in a high temperature environment, whichdissociation occurs within the adhesive composition. This causes animprovement in the adhesive strength at a high temperature, and evenafter the high-temperature process is carried out to the adhesivecomposition, the adhesive composition can be easily stripped off.Further, it is possible to restrain a content of a carboxyl group in theaforementioned polymer to be low, which carboxyl group causes a decreasein alkaline resistance. As a result, the adhesive composition containingthe polymer as a main component has high alkaline resistance.

Consequently, it is possible to provide an adhesive composition whichhas more improved heat resistance, alkaline resistance, and adhesivestrength in a high temperature environment, and which allows an adhesivelayer made from the adhesive composition to be more easily stripped offafter the adhesive layer has been subjected to a high-temperatureprocess.

The bifunctional monomer in the present specification denotes acompound, which has two functional groups. Namely, the bifunctionalmonomer is not limited as long as the bifunctional monomer is acompound, which has two functional groups. However, it is preferable forthe bifunctional monomer to be at least one of a bifunctional monomerselected from the group consisting of compounds represented by GeneralFormula (2) as follows:

Chem. 2X¹—R⁴—X²   (2)(where R⁴ is an organic group selected from a divalent C2 to C20 alkylgroup and a divalent C6 to C20 organic group having a cyclic structure,and may have an oxygen atom; X¹ and X² are independently a(meth)acryloyl group or a vinyl group). Examples of the compoundsrepresented by General Formula (2) encompass: dimethylol-tricyclodecanediacrylate, neopentyl glycol diacrylate, 1,9-nonanediol acrylate,naphthalene diacrylate, dicyclopentanyl diacrylate, and compoundsrepresented by Formula (3) as follows:

(where R⁵ and R⁶ independently represent ethylene oxide or propyleneoxide; and n and s independently represent an integer of 0 to 4). Thesecompounds may be used solely, or two or more of the compounds may beused in combination.

Among these bifunctional monomers, it is further preferable for thebifunctional monomer to be at least one bifunctional monomer selectedfrom the group consisting of dimethylol-tricyclodecane diacrylate,neopentyl glycol diacrylate, 1,9-nonanediol acrylate, naphthalenediacrylate, dicyclopentanyl diacrylate, and the compounds represented bythe Formula (3). These bifunctional monomers can be readily cross-linkedwith other monomer composition components, and crosslinking structuresof such cross-linked bifunctional monomers are stable. Therefore, it ispossible to obtain an adhesive composition which has further improvedadhesive strength in a high temperature environment and further improvedheat resistance.

In a case where the adhesive composition of the present inventioncontains the bifunctional monomer, an amount of the bifunctional monomermay be set as appropriate in accordance with aimed properties of theadhesive composition such as aimed adhesive strength. However, theamount of the bifunctional monomer is preferably in a range of 0.1 to0.5 parts by weight, further preferably in a range of 0.1 to 0.3 partsby weight, where a total amount of the maleimide group-containingmonomer, the styrene, and the alkyl(meth)acrylate is 100 parts byweight. The amount in the range of 0.1 to 0.5 parts by weight canfurther improve the adhesive strength in a high temperature environmentand the heat resistance of an obtained adhesive composition. The amountin that range can also suppress moisture absorption, thereby making itpossible to prevent gelling of the adhesive composition.

(Components other than Main Component in Adhesive Composition)

The adhesive composition according to the present embodiment may furtherinclude, to an extent in which essential properties of the presentinvention is not lost, miscible additives, for example, a commonly usedaddition resin, plasticizing agent, adhesive auxiliary agent,stabilization agent, coloring agent, and surface active agent, each ofwhich improves effectiveness of the adhesive.

Further, the adhesive composition may be diluted by use of an organicsolvent for adjusting viscosity of the adhesive composition, in theextent in which the essential properties of the present invention is notlost. Examples of the organic solvent encompass: ketones such asacetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, and2-heptanone; polyhydric alcohols and derivatives thereof such asmonomethyl ethers, monoethyl ethers, monopropyl ethers, monobutylethers, or monophenyl ethers of ethylene glycol, ethylene glycolmonoacetate, diethylene glycol, diethylene glycol monoacetate, propyleneglycol, propylene glycol monoacetate, dipropylene glycol, or dipropyleneglycol monoacetate; cyclic ethers such as dioxane; and esters such asmethyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butylacetate, methyl pyruvate, ethyl pyruvate, methyl methoxy propionate, andethyl ethoxy propionate. These organic solvents may be used solely, ortwo or more of the organic solvents may be used in combination.Particularly, it is more preferable to use the polyhydric alcohols andderivatives thereof such as the monomethyl ethers, monoethyl ethers,monopropyl ethers, monobutyl ethers, and monophenyl ethers of ethyleneglycol, ethylene glycol monoacetate, diethylene glycol, diethyleneglycol monoacetate, propylene glycol, propylene glycol monoacetate,dipropylene glycol, or dipropylene glycol monoacetate.

An amount of the organic solvent is set as appropriate in accordancewith a film thickness of the adhesive composition to be applied, and isnot particularly limited as long as the adhesive composition is in aconcentration in which the adhesive composition can be applied to asupporting body such as a semiconductor wafer or the like. Generally,the adhesive composition is used so that a solid content concentrationis in a range of 20 wt % to 70 wt %, and more preferably in a range of25 wt % to 60 wt %.

[Preparing Method of Adhesive Composition]

(Copolymerization Reaction)

The copolymerization reaction of the monomer composition may be carriedout by a publicly known method, and is not especially limited. Forexample, the polymer that is a main component of the adhesivecomposition of the present invention can be obtained by stirring themonomer composition by use of an existing stirring device.

A temperature condition in the copolymerization reaction may be set asappropriate and is not limited. However, the temperature condition ispreferably in a range of 60 to 150° C., further preferably in a range of70 to 120° C.

In the copolymerization reaction, a solvent may be used as appropriate.The aforementioned organic solvents can be used as the solvent. Amongthe aforementioned organic solvents, propylene glycol monomethyl etheracetate (hereinafter, referred to as “PGMEA”) is more preferable.

In the copolymerization reaction according to the present embodiment, apolymerization initiator may be used as appropriate. Examples of thepolymerization initiator encompass: azo compounds such as2,2′-azobisisobutylonitrile, 2,2′-azobis(2-methylbutylonitrile),dimethyl 2,2′-azobis isobutyrate,1,1′-azobis(cyclohexane-1-carbonitrile), and 4,4′-azobis(4-cyanovalericacid); and organic peroxides such as decanoyl peroxide, lauroylperoxide, benzoyl peroxide, bis(3,5,5-trimethyl hexanoyl) peroxide,succinic acid peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butylperoxypivalate, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate.These polymerization initiators may be used solely, or two or more ofthe polymerization initiators may be used in combination as appropriate.An amount of the polymerization initiator to be used may be set asappropriate in accordance with a combination of the monomer composition,reaction conditions, and the like, and is not particularly limited.

A weight-average molecular weight of the polymer used in the presentinvention is preferably in a range of 10000 to 300000, more preferablyin a range of 20000 to 200000, and especially preferably in a range of30000 to 150000. The range of not less than 10000 allows an obtainedadhesive composition to have good flexibility, and the range of not morethan 300000 allows an obtained adhesive composition to have good heatresistance.

(Addition of Thermal Polymerization Inhibitor)

A method for adding the thermal polymerization inhibitor to the polymermay be carried out by a publicly known method, and is not especiallylimited. For example, after copolymerization reaction is completed, thethermal polymerization inhibitor may be added, at once or stepwise, tothe copolymerization reaction system, that is, a reaction container inwhich the copolymerization reaction has been carried out. Further, thethermal polymerization inhibitor may be dissolved in an appropriateorganic solvent and then added.

[Film Adhesive]

The adhesive composition according to the present invention as describedabove may be used in various ways depending on its purpose. For example,the adhesive composition in a liquid form may be applied on a processedbody such as a semiconductor wafer so as to form an adhesive layer.Alternatively, a film adhesive according to the present invention, thatis, a film such as a flexible film on which an adhesive layer containingany one of the foregoing adhesive compositions is formed in advance anddried, may be used by attaching this film (film adhesive) to theprocessed body (film adhesive method).

As such, the film adhesive according to the present invention includes afilm, and an adhesive layer provided on the film, containing any one ofthe aforementioned adhesive compositions.

Since the monomer composition further contains the maleimidegroup-containing monomer, the heat resistance of the adhesivecomposition constituting the adhesive layer is improved. As a result, itis possible to obtain a film adhesive that excels in heat resistance andadhesive strength in a high temperature environment.

Further, the adhesive composition contains the thermal polymerizationinhibitor as such, thereby improving solubility of the adhesive layer.As a result, it is possible to obtain a film adhesive that is easilystripped off.

The film adhesive may be used such that a protection film is furtherprovided on the adhesive layer. In this case, the adhesive layer iseasily provided on a processed body by (i) stripping off the protectionfilm which covers the adhesive layer; (ii) placing, on the processedbody, the adhesive layer thus exposed, and (iii) stripping off the filmfrom the adhesive layer.

Consequently, the use of the film adhesive allows formation of anadhesive layer having an even thickness and a good surface smoothness ascompared to a case where the adhesive composition is directly applied ona processed body so as to form an adhesive layer.

The film to be used in manufacture of the film adhesive is not limited,as long as an adhesive layer formed on the film is strippable from thefilm and the film is a release film which can transfer the adhesivelayer to a surface to be processed of a protection board, a wafer, orthe like. An example of the film is a flexible film made of a syntheticresin film such as polyethylene terephthalate, polyethylene,polypropylene, polycarbonate or polyvinyl chloride, and having athickness of 15 μm to 125 μm. It is preferable for the film to bestrip-processed if necessary so that transfer can be readily carriedout.

A publicly known method may be appropriately used as a method forforming the adhesive layer on the film in accordance with a thickness oran evenness of a desired adhesive layer. An example of the method is amethod in which the adhesive composition of the present invention isapplied on the film so that a dried film thickness of the adhesive layeris 10 to 1000 μm.

In a case where the protection film is to be used, the protection filmto be used is not limited as long as the film is strippable from theadhesive layer. However, it is preferable for the protection film to be,for example, a polyethylene terephthalate film, a polypropylene film, ora polyethylene film. Moreover, the protective film is preferably coatedwith silicon or baked. This allows the protective film to be easilystripped off from the adhesive layer. A thickness of the protection filmis not particularly limited, however is preferably in a range of 15 μmto 125 μm. This is because the adhesive film attached to the protectivefilm can secure flexibility of the film adhesive.

A method of using the film adhesive is not particularly limited. Forexample, the following method may be taken in a case where theprotection film is used: (i) the protection film is stripped off fromthe film adhesive, (ii) the adhesive layer thus exposed is placed on asurface of a processed body, and (iii) a heating roller is rolled on thefilm (a back surface of the surface on which the adhesive layer isformed), so that the adhesive layer is thermally compressed onto thesurface of the processed body. At this time, by sequentially rolling upthe protection film on a roller such as a reel roller, the protectionfilm that is stripped off from the film adhesive may be stored andreused.

The adhesive composition of the present embodiment is not particularlylimited as long as the adhesive composition is used for adheringpurposes. However the adhesive composition is suitably used as anadhesive composition for adhering a high-precision processing protectionboard of a semiconductor wafer to a substrate such as a semiconductorwafer. The adhesive composition of the present invention is particularlysuitably used as an adhesive composition, when a substrate such as thesemiconductor wafer is grinded so that a thickness of the substrate isreduced, for attaching the substrate to a support plate (e.g., JapanesePatent Application Publication, Tokukai, No. 2005-191550A (PublicationDate: Jul. 14, 2005)).

[Stripping Solution]

A commonly used stripping solution may be used as a stripping solutionfor removing the adhesive composition according to the presentembodiment, that is, as a stripping solution for dissolving the adhesivecomposition and stripping off an adhesive layer made from the adhesivecomposition. However from a point of environmental burden and astripping property, a stripping solution whose main component is PGMEA,ethyl acetate, or methyl ethyl ketone is preferably used.

[Heat Treatment Method]

A heat treatment method of the present invention includes the step ofheating a material to be heated including the adhesive composition at atemperature in a range of 250° C. to 350° C.

Moreover, the heat treatment method of the present invention includesthe steps of: forming an adhesive layer from the adhesive composition ona surface of a substrate; heating the substrate at a temperature in arange of 250° C. to 350° C.; and stripping off the adhesive layer fromthe substrate.

Firstly, an adhesive layer is formed on a substrate by use of theadhesive composition of the present invention (a forming step). A methodfor forming the adhesive layer is not especially limited, but may be forexample, a method for forming an adhesive layer by use of theaforementioned film adhesive, a method for directly applying theadhesive composition by use of a publicly known technique, such as anapplicator or a bar coater, or the like method. These methods allowforming of an adhesive coating film having an excellently-uniform filmthickness.

After the adhesive layer is formed on the substrate, a material to beheated is adhered onto the adhesive layer. Then, an intended heattreatment is carried out with respect to the material to be heated thatis adhered to the substrate (a heat treatment step). A temperatureduring the heat treatment can be determined as appropriate in accordancewith what kind of treatment is carried out with respect to the materialto be heated. However, the temperature is preferably not less than 250°C., more preferably not less than 250° C. but not more than 350° C.Further, the heat treatment may be carried out in high vacuum (forexample, 3 Pa). By carrying out the heat treatment at the temperature,the adhesive composition of the present invention can successfullyexhibit effects of adhesiveness at a high temperature and easiness instripping off after a high-temperature process has been carried out.

After the material to be heated has been subjected to the heattreatment, the adhesive layer is dissolved and stripped off by use ofthe aforementioned stripping solution such as PGMEA so that the materialto be heated is stripped off from the substrate (a stripping step).

In the heat treatment method of the present invention, the adhesivecomposition of the present invention is used. Therefore, the adhesivestrength is successfully maintained even at a high temperature of 250°C. Further, even after the adhesive layer has been processed at atemperature of not less than 250° C. and in high vacuum of 3 Pa, theadhesive layer can be easily stripped off.

A purpose of the heat treatment method of the present invention is notespecially limited as long as the adhesive composition of the presentinvention is used for the heat treatment. However, the heat treatmentmethod of the present invention is favorably applicable to a series ofprocesses of: (i) adhering a protection board for use in high-precisionprocessing of a semiconductor wafer, to a substrate such as asemiconductor wafer, (ii) carrying out a high-temperature process, andsubsequently (iii) separating the protection board from thesemiconductor wafer.

The following deals with examples of the present invention. However, thepresent invention is not limited to these examples.

EXAMPLES

Firstly explained is a method for preparing an adhesive composition ofExample 1 in detail.

Into a 300 ml four-neck flask equipped with a reflux condenser, astirrer, a thermometer, and a nitrogen inlet tube, (i) 111.6 g of PGMEAas a solvent, and (ii) as shown in Table 1, 30 g of methyl methacrylate,52 g of styrene, and 18 g of cyclohexylmaleimide, those as monomers,were added, and blowing of N₂ into the flask was initiated. A mixture inthe flask was stirred so that polymerization was initiated. While themixture was being stirred, a temperature in the flask was increased to100° C. Then, a mixed solution containing 13.33 g of PGMEA and 1 g oft-butyl peroxy 2-ethylhexanoate (a polymerization initiator) wascontinuously dropped via a dropping nozzle into the flask over 4 hours.A dropping speed was constant.

After the dropping was completed, an obtained polymerization reactionsolution was left for aging at 100° C. for 1 hour. Then, a mixedsolution containing 25.10 g of PGMEA and 0.3 g of t-butyl peroxy2-ethylhexanoate was dropped into the polymerization reaction solutionover 1 hour. After the polymerization reaction solution was further leftfor aging at 100° C. for 1 hour, 1.0 g of 1,1,3,3-tetramethylbutylperoxy2-ethylhexanoate was added to the solution at once. Subsequently, thepolymerization reaction solution was left for aging at 100° C. for 3hours. After a temperature of the polymerization reaction solution wasincreased until a reflux of the solvent was observed, the polymerizationreaction solution was left for aging for 1 hour. After that, thepolymerization was terminated. In this way, a resin 1 was synthesized.

Further, an adhesive composition of Example 4 was prepared as follows.

Into a 300 ml four-neck flask equipped with a reflux condenser, astirrer, a thermometer, and a nitrogen inlet tube, (i) 111.6 g of PGMEAas a solvent, and (ii) as shown in Table 1, 58 g of methyl methacrylate,20 g of styrene, and 18 g of cyclohexylmaleimide, those as monomers,were added, and blowing of N₂ into the flask was initiated. A mixture inthe flask was stirred so that polymerization was initiated. While themixture was being stirred, a temperature in the flask was increased to100° C. Then, (i) a mixed solution containing 13.3 g of PGMEA and 20 gof styrene and (ii) a mixed solution containing 13.3 g of PGMEA and 0.6g of t-butyl peroxy 2-ethylhexanoate were continuously dropped viadropping nozzles, respectively, into the flask over 4 hours. A droppingspeed was constant. After the dropping was completed, an obtainedpolymerization reaction solution was subjected to the same treatments asthose carried out with respect to the resin 1 of Example 1. In this way,a resin 4 was synthesized.

Resins 2 of Examples 2, 6, and 7, a resin 3 of Example 3, and a resin 6of Comparative Example 1 were synthesized in the same manner as theresin 1 of Example 1. A resin 5 of Example 5 was synthesized in the samemanner as the resin 4 of Example 4.

As such, in Example 1 through 3, Examples 6 and 7, and ComparativeExample 1, after a monomer composition was wholly mixed in advance,copolymerization reaction was initiated. On the other hand, in Examples4 and 5, part of styrene to be used (Example 4) or all styrene to beused (Example 5) was mixed into a flask after components other than thepart of or all the styrene, of the monomer composition, had been mixedin the flask and polymerization had been initiated.

Further, resins 7 and 8 of Examples 8 through 13 and Comparative Example2 and a resin 9 of Example 14 were synthesized in the same manner as theresin 1 of Example 1. In Example 14, in synthesizing the resin 9,dicyclopentanyl diacrylate was also mixed, as a bifunctional monomer,with a monomer composition. In this way, in Examples 8 through 14 andComparative Example 2, after a monomer composition was wholly mixed inadvance, copolymerization reaction was initiated.

Moreover, resins 10 of Example 15 and Comparative Example 3, resins 11of Example 16 and Comparative Example 4, and resins 12 of Examples 17and 18 and Comparative Example 5 were synthesized in the same manner asthe resin 4 of Example 4 except that phenylmaleimide was also mixed as amonomer before polymerization was initiated. In Examples 15 through 18and Comparative Example 3 through 5, all styrene to be used was mixedinto a flask after components other than the styrene, of a monomercomposition, had been mixed in the flask and polymerization had beeninitiated.

Tables 1 through 3 show compositions of monomer compositions in Examplesand Comparative Examples and weight-average molecular weights of theresins obtained by polymerizing the monomer compositions, respectively.

TABLE 1 Composition Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Com. Ex. 1(mass ratio) (Resin 1) (Resin 2) (Resin 3) (Resin 4) (Resin 5) (Resin 2)(Resin 2) (Resin 6) Methyl methacrylate 30 40 80 58 58 40 40 30 Styrene(Random) 52 42 0 20 0 42 42 52 Styrene 0 0 0 20 40 0 0 0 (Mixed afterinitiation of synthesis reaction) Cyclohexylmaleimide 18 18 20 18 18 1818 18 Weight-average molecular 82000 80000 80000 80000 80000 80000 8000082000 weight

TABLE 2 Composition Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Com.Ex. 2 (mass ratio) (Resin 7) (Resin 7) (Resin 7) (Resin 7) (Resin 8)(Resin 8) (Resin 9) (Resin 7) Methyl methacrylate 50 50 50 50 50 50 5050 Styrene (Random) 32 32 32 32 32 32 32 32 Styrene 0 0 0 0 0 0 0 0(Mixed after initiation of synthesis reaction) Cyclohexylmaleimide 18 1818 18 18 18 18 18 Dicyclopentanyl diacrylate 0 0 0 0 0 0 0.7 0Weight-average molecular 80000 80000 80000 80000 118000 118000 18000080000 weight

TABLE 3 Composition Ex. 15 Com. Ex. 3 Ex. 16 Com. Ex. 4 Ex. 17 Ex. 18Com. Ex. 5 (mass ratio) (Resin 10) (Resin 10) (Resin 11) (Resin 11)(Resin 12) (Resin 12) (Resin 12) Methyl methacrylate 50 50 30 30 50 5050 Styrene (Random) 0 0 0 0 0 0 0 Styrene 32 32 30 30 10 10 10 (Mixedafter initiation of synthesis reaction) Cyclohexylmaleimide 10 10 20 2020 20 20 Phenylmaleimide 8 8 20 20 20 20 20 Weight-average molecular86000 86000 86000 86000 81000 81000 81000 weight *Abbreviation: Ex.stands for Example. Com. Ex. stands for Comparative Example.

Each of the resins 1 through 12 and a thermal polymerization inhibitorwere dissolved in PGMEA so as to prepare an adhesive composition inwhich a concentration of the polymer was 40 wt %. Tables 4 through 6show an amount of the thermal polymerization inhibitor to be added ineach of Examples and Comparative Examples. IRGANOX1010 (manufactured byCiba Speciality Chemicals Corporation) was used as the thermalpolymerization inhibitor.

TABLE 4 Additive amount of thermal polymerization inhibitor Ex. 1 Ex. 2Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Com. Ex. 1 With respect to 1 pt. wt. 1 pt.wt. 1 pt. wt. 1 pt. wt. 1 pt. wt. 2 pts. wt. 4 pts. wt. Not 100 pt. wt.added

TABLE 5 Additive amount of thermal polymerization Com. inhibitor Ex. 8Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 2 With respect to 1 pt. wt.3 pts. wt. 5 pts. wt. 10 pts. wt. 1 pt. wt. 5 pts. wt. 5 pts. wt. Not100 pt. wt. added

TABLE 6 Additive amount of thermal polymerization inhibitor Ex. 15 Com.Ex. 3 Ex. 16 Com. Ex. 4 Ex. 17 Ex. 18 Com. Ex. 5 With respect to 5 pts.wt. Not 5 pts. wt. Not 1 pt. wt. 5 pts. wt. Not 100 pt. wt. added addedadded *Abbreviation: Ex. stands for Example. Com. Ex. stands forComparative Example. pt(s). wt. stands for part(s) by weight.

The adhesive compositions according to Examples 1 through 18 andComparative Examples 1 through 5 were applied on 6-inch silicon wafers,respectively, and dried at 110° C., 150° C., and then 200° C., each for3 minutes, that is, dried for 9 minutes in total. In this way, coatingfilms having a thickness of 15 μm were formed on the silicon wafers,respectively.

The following explains about measurement results on the adhesivecompositions thus applied on the silicon wafers.

(Evaluation of Heat Resistance and Measurement of Degassing Amount)

A temperature of each of the coating films was increased from 40° C. to250° C. and an amount (degassing amount) of gas generated from each ofthe coating films was measured. Heat resistance of each of the adhesivecomposition was evaluated from the degassing amount.

A reason why heat resistance can be evaluated from the degassing amountis as follows. That is, a degassing amount measured until a temperatureincreased to 100° C., is an amount of gas derived from either watervapor or its azetropic gas. The water vapor or the azetropic gas isderived from moisture absorbed by the adhesive composition. On the otherhand, a degassing amount measured at a temperature of not less than 100°C. is derived from gas that has been generated due to decomposition ofthe adhesive composition caused by heat. Therefore, the heat resistancecan be evaluated from the degassing amount at a temperature of not lessthan 100° C., particularly around 200° C.

A TDS method (Thermal Desorption Spectroscopy method) was employed forthe measurement of the degassing amount. EMD-WA1000 (manufactured byESCO, Ltd.) was used as a TDS measuring device (discharged gas measuringdevice).

A measuring condition of the TDS device was set as Width: 100; CenterMass Number: 50; Gain: 9; Scan Speed: 4; and Emult Volt: 1.3 KV.

The heat resistance was evaluated at a temperature of 200° C. based ondefinitions as follows: “G (good)” indicates a case where a strength(Indensity) found by the TDS measuring device was less than 100000, andno residue was observed by a metallurgical microscope; “S (sufficient)”indicates a case where the Indensity was not less than 100000, howeverno residue was observed by the metallurgical microscope; and “P (poor)”indicates a case where the Indensity was not less than 100000 and aresidue was observed by the metallurgical microscope.

Further, the degassing amount was evaluated at 200° C. based ondefinitions as follows: “G” indicates a case where a strength(Indensity) found by the TDS measuring device was less than 100000; and“P” indicates a case where the Indensity was not less than 100000.

(Evaluation of Flexibility)

Firstly, it was observed by eye whether or not there were cracks oncoated film layers applied on the silicon wafers, respectively. A coatedfilm layer that had a crack was evaluated as “P”; and a coated filmlayer that had no crack was evaluated as “G”.

Subsequently, a heat cycle test was carried out with respect to each ofthe silicon wafers by use of a thermal shock test device, TSE-11A(manufactured by ESPEC Corp.). After the heat cycle test, it wasobserved whether or not there were cracks on the silicon wafers toevaluate flexibilities of the adhesive compositions. The heat cycle testwas carried out as follows. Each of the resins was maintained at −30° C.for 30 minutes and then at +80° C. for 30 minutes, as one cycle, andthis process was repeated five times in total. After the heat cycletest, whether or not there were cracks on the coated film layers wasobserved by eye. A coated film layer that had a crack was evaluated as“P”; and a coated film layer that had no crack was evaluated as “G”.

(Evaluation of Solubility with Heat Resistance and Measurement ofDissolution Rate)

After the silicon wafers were heated at 250° C. for 1 hour, the siliconwafers were immersed in PGMEA. After the immersion, it was observed byeye whether the coated film layers were dissolved or not. A coated filmlayer that was dissolved was evaluated as “G”; and a coated film layerthat was not dissolved was evaluated as “P”.

Further, a dissolution rate (nm/sec) was calculated from a relationshipbetween a thickness of a coated film layer that was dissolved and adissolution time.

(Evaluation of Adhesive Strength)

Glass substrates were adhered to the coated film layers of the adhesivecompositions, provided on the silicon wafers, respectively, at 200° C.with a load of 1 kg. The glass substrates were pulled, and adhesivestrengths at a time when the glass substrates were stripped off from thesilicon wafers, respectively, were found by use of a vertical modelmotorized stand “MX-500N” (manufactured by IMADA CO., LTD.). An adhesivecomposition whose adhesive strength at 250° C. was not less than 2kg/cm² was evaluated as “G”; and an adhesive composition whose adhesivestrength at 250° C. was less than 2 kg/cm² was evaluated as “P”.

The adhesive compositions of Examples 1 through 18 and ComparativeExamples 1 through 5 were compared in terms of adhesive strength at 250°C., generated gas, heat resistance, flexibility, solubility with heatresistance, and a dissolution rate. Tables 7 through 9 show results ofthe comparison.

TABLE 7 Evaluation Ex. Com. Result Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 7Ex. 1 Adhesive G G G G G G G G Strength at High Temperature (250° C.)Generated Gas G G G G G G G G Heat Resistance G G G G G G G GFlexibility (After G G G G G G G G application) Flexibility (After P G GG G G G P heat cycle test) Solubility with G G G G G G G P HeatResistance (250° C., 1 hour) Dissolution rate 80 75 60 80 80 76 74 0(nm/sec)

TABLE 8 Evaluation Ex. Ex. Ex. Ex. Ex. Com. Result Ex. 8 Ex. 9 10 11 1213 14 Ex. 2 Adhesive G G G G G G G G Strength at High Temperature (250°C.) Generated Gas G G G G G G G G Heat Resistance G G G G G G G GFlexibility (After G G G G G G G G application) Flexibility (After G G GG G G G G heat cycle test) Solubility with G G G G G G G P HeatResistance (250° C., 1 hour) Dissolution rate 77 77 76 75 68 66 66 0(nm/sec)

TABLE 9 Evaluation Ex. Com. Ex. Com. Ex. Ex. Com. Result 15 Ex. 3 16 Ex.4 17 18 Ex. 5 Adhesive G G G G G G G Strength at High Temperature (250°C.) Generated Gas G G G G G G G Heat Resistance G G G G G G GFlexibility (After G G G G G G G application) Flexibility (After G G P PG G G heat cycle test) Solubility with G P G P G G P Heat Resistance(250° C., 1 hour) Dissolution rate 65 0 40 0 20 20 0 (nm/sec)*Abbreviation: Ex. stands for Example. Com. Ex. stands for ComparativeExample.

In regard to the wafer of Example 7, after the wafer was heated at 300°C. for 1 hour, the “evaluation of solubility with heat resistance” wascarried out with respect to the adhesive composition of Example 7 in thesame manner as above. As a result of the evaluation, it was observedthat the adhesive composition was dissolved (a dissolution speed: 83nm/sec).

As shown in Tables 7 through 9, it was demonstrated that Examples of thepresent invention exhibited good solubility with heat resistance and thecoated film layers of Examples were dissolved even after the coated filmlayers had been heated at a high temperature of 250° C. Further, it wasfound that the coated film layer of Example 7 was dissolved even afterthe coated film layer was heated at a high temperature of 300° C. Incontrast, in Comparative Examples 1 through 5, the coated film layerswere not dissolved.

The measurement of flexibility of an adhesive composition that has beensubjected to the heat cycle test is a flexibility measurement carriedout under tougher conditions. Therefore, even if a crack was observed inthe flexibility measurement under such tougher conditions, there occursno problem in terms of use of the adhesive composition of the presentinvention.

As described above, an adhesive composition of the present invention isan adhesive composition (a) whose main component is a polymer obtainedby copolymerizing a monomer composition containing a monomer having amaleimide group and (b) which further contains a thermal polymerizationinhibitor. This allows an obtained adhesive composition to have, in amain chain of the polymer, an imide ring derived from the monomer havinga maleimide group. As a result, (i) heat resistance at a hightemperature, (ii) adhesiveness in a high temperature environment(especially, at 200° C. to 250° C.), and (ii) alkaline resistance, ofthe obtained adhesive composition, are improved.

Moreover, the adhesive composition further contains a thermalpolymerization inhibitor. As a result, thermal polymerization isrestrained during a high-temperature process (especially, at 250° C. and3 Pa), thereby resulting in that it is possible to easily strip off anadhesive layer made from the adhesive composition, even after theadhesive layer has been subjected to a high-temperature process.

In this way, the present invention makes it advantageously possible toprovide an adhesive composition (i) which excels in heat resistance,adhesive strength in a high temperature environment (especially, 200° C.to 250° C.), and alkaline resistance and (ii) which allows an adhesivelayer made from the adhesive composition to be easily stripped off evenafter the adhesive layer has been subjected to a high-temperatureprocess in which the adhesive layer is heated at 250° C. for 1 hour.

An adhesive composition and a film adhesive, according to the presentinvention, (i) have high heat resistance, (ii) generate little gas whilebeing heated, (iii) excel in adhesive strength at a high temperature,and (iv) are excellently dissolved even after a high-temperature processhas been carried out. As a result, the adhesive composition and the filmadhesive of the present invention can be favorably used in processing ofa semiconductor wafer or a chip which processing requires ahigh-temperature process.

The embodiments and concrete examples of implementation discussed in theforegoing detailed explanation serve solely to illustrate the technicaldetails of the present invention, which should not be narrowlyinterpreted within the limits of such embodiments and concrete examples,but rather may be applied in many variations within the spirit of thepresent invention, provided such variations do not exceed the scope ofthe patent claims set forth below.

The invention claimed is:
 1. An adhesive composition dissolved in anorganic solvent, wherein the adhesive composition comprises: (1) as amain component, a polymer obtained by copolymerizing a monomercomposition comprising (i) an alkyl (meth)acrylate, (ii) a monomerhaving a maleimide group, and (iii) styrene, and (2) a thermalpolymerization inhibitor, wherein the monomer having a maleimide groupis contained in the monomer composition in an amount of not less than5.0 wt. % but not more than 20 wt. %, wherein an amount of the alkyl(meth)acrylate in the monomer composition is not less than 30 parts byweight but not more than 58 parts by weight, an amount of the styrene inthe monomer composition is not less than 30 parts by weight but not morethan 60 parts by weight, and the total amount of the monomer compositionis 100 parts by weight, and wherein the adhesive composition remainssoluble in propylene glycol monomethyl ether acetate even if theadhesive composition is heated at 250° C. for 1 hour.
 2. The adhesivecomposition as set forth in claim 1, wherein: the thermal polymerizationinhibitor is contained in the adhesive composition by not less than 0.1wt. % but not more than 10.0 wt. %.
 3. The adhesive composition as setforth in claim 1, wherein: the thermal polymerization inhibitor is aphenolic thermal polymerization inhibitor.
 4. The adhesive compositionas set forth in claim 1, wherein: the polymer has a styrene blocksegment.
 5. The adhesive composition as set forth in claim 1, wherein: amass ratio of the alkyl (meth)acrylate with respect to the styrene iswithin a range of 0.1:1 to 3:1.
 6. A film adhesive comprising: a film;and an adhesive layer provided on the film, comprising the adhesivecomposition as set forth in claim
 1. 7. The adhesive composition as setforth in claim 1, wherein the monomer having a maleimide group is amonomer represented by formula (1)

wherein R¹ and R² independently represent a hydrogen atom or a C1through C20 organic group, and the organic group may contain an oxygenatom, a nitrogen atom, a sulfur atom, or a halogen atom; and R³represents an alkyl group, an alicyclic hydrocarbon group, or an arylgroup.
 8. The adhesive composition as set forth in claim 1, furthercomprising a compound having two functional groups.
 9. A heat treatmentmethod comprising the step of heating a material to be heated at atemperature in a range from 250° C. to 350° C., wherein the material tobe heated is an adhesive composition comprising: (1) as a maincomponent, a polymer obtained by copolymerizing a monomer compositioncomprising (i) an alkyl (meth)acrylate, (ii) a monomer having amaleimide group, and (iii) styrene, and (2) a thermal polymerizationinhibitor, wherein the monomer having a maleimide group is contained inthe monomer composition in an amount of not less than 5.0 wt. % but notmore than 20 wt. %, wherein an amount of the alkyl (meth)acrylate in themonomer composition is not less than 30 parts by weight but not morethan 58 parts by weight, an amount of the styrene in the monomercomposition is not less than 30 parts by weight but not more than 60parts by weight, and the total amount of the monomer composition is 100parts by weight, and wherein the adhesive composition remains soluble inpropylene glycol monomethyl ether acetate even if the adhesivecomposition is heated at 250° C. for 1 hour.
 10. The heat treatmentmethod as set forth in claim 9, comprising the steps of: (a) forming anadhesive layer from the adhesive composition on a surface of asubstrate; (b) heating the substrate at a temperature in a range of 250°C. to 350° C. after the step (a); and (c) stripping off the adhesivelayer from the substrate after the step (b).